Telephone system



2 Sheets-Sheet 1 F. L. KAHN TELEPHONE SYSTEM Filed April 13. 1932 ll. d c g fi m M F IIIIJ QN IHEEH Frederick L. Kahn Fifi 1 July 24, 1934.

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Filed April 15, 1932 2 Sheets-Sheet 2 Frederick L. Kahn Patented July 24, 1934 UNITED STATES PATENT OFFICE/U TELEPHONE SYSTEM Frederick L. Kahn, Chicago, 111., assignor, by

mesne assignments, to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application April 13, 1932, Serial No. 604,976

19 Claims. (01. 179*27) This invention relates in general to automatic Description of drawings telephone systems and its object, broadly stated, i is to provide new and improved switching appa- The accompanying drawmgs: comprlsmg F ratus for automatic telephone systems provided 1 and Show by means of the usual i i 5 ith Secretarial Service. diagrams a sufiicient amount of equipment in a 0 system embodying the features of the invention I General descrwtwn to permit the invention to be readily understood. More specifically, an object of the present in- Fig. 1 shows a subscribers substation A, an

7 pvention is the provision of switching apparatus exchange distributing frame DF, and a portion 10 in the telephone exchange that can be controlled of the regular exchange equipment for the line 65 by'subscribers in the telephone system so that at substation A. The secretarial equipment in subsequent calls to their stations can be interthe exchange is also shown, and comprises the cepted and answered by an operator (or' secresubscribers individual apparatus units, such as V tary) at the central ofiice. SU, the finder switch FS, and trunk circuit TC, 16 Telephone companies can install the equipboth of which are common to a plurality of sub- 76 ment for this type of service without making any scribers individual apparatus units, such as SU. changes in the regular exchange equipment or Fig. 2 shows a finder switch F531 and a trunk the subscribers substation equipment. As many circuit TCl, which are modifications of finder secretarial service lines as desired are wired to switch FS and trunk circuit TC shown in Fig. 1. H

' 20 the exchange distributing frame and are con- The trunk circuit TCl contains a register ar- 15 nected at this point to the line of the subscriber ranged to be set automatically to the same pocontracting for the service merely by running a sition as the finder FSl so as to inform-the jumper from the contracting subscribers conoperator in each case of the identity of the connector bank terminal to the secretarial service nected subscribers line. I x

line equipment. It is contemplated that this Referring now particularly to Fig. 1, there is service will be contracted for by subscribers in shown therein a subscribers substation Abridged the telephone system for a regular term (month across condutcors 30 and 31, the usual distributor year), or on a temporary basis to be charged ing frame DB in the telephone exchange for either by the day or by the number of calls hancross-connecting the subscribers line to the con- 30 dled during the period the secretarial service is ductors extending to the individual lineswitch, s5 and to the connector-bank terminals over which A special feature of the present invention is connections are established with the subscriber at that this type of service is made available to substation A. "party-line subscribers, as well as to individual- The subscriber at substation A may establish line subscribers. connections with other subscribers in the tele- In a secretarial system of the type disclosed, phone exchange over his individual lineswitch LS, it is entirely within the control of a contracting selectors, such as S, and connectors (not shown). subscriber to associate the operator (or se'cre- The ring-back switch RBS, similar to the one tary) with his line, as well as to dispense with shown in Fig..10 of Patent No. 1,805,726, granted "-40 the operator whenever he wishes to answer the to Norman H. Saunders, May 19, 1931, is one of calls himself. Furthermore, during the period a group usually provided in automatic telephone the operator is connected to the line, the subsystems to permit a subscriber on a harmonic- 'scriber can use his telephone for incoming and ringing party line to selectively signal other suboutgoing calls in the regular manner. In the scribers on the same line. It is well known to '45 case of incoming calls during such time, it is those familiar with the art that after a calling merely a question of who answers the call firstsubscriber has set the ring-back switch and has that is, the subscriber or the operator. When an replaced his receiver, the ring-back switch will incoming call is answered by the subscriber after cause ringing current of two difierent frequencies the operator has answered, the operator can reto be alternately transmitted back over the party 50 lease her connection and let the subscriber hanline to. signal the calling subscriber and the dle the call. called subscriber on the same line. In the present Various features relating to the operation of invention the ring-back switch is utilized for the the system will not be specifically mentioned at purpose of connecting and disconnecting sub-- this time, but will be described in the specificascribers contracting for secretarial service to and 55 -tion and-pointed out in the appended claims. from the secretarial equipment. This will be more apparent by further perusal of the specification.

The subscribers individual apparatus unit SU comprises three harmonic ringers, each of which responds to a different ringing frequency, and associated relays. Each subscriber that has contracted for secretarial service has his line jumpered, at the distributing frame DF, to a subscribers unit, similar to the subscribers unit SU shown on the drawings.

Fig. 1 also shows a finder switch FS having three line wipers, which is of the well-known single-level rotary type of switch. This switch is only one of a group of similar switches, all of which may be controlled to connect the secretarial operator to the subscribers line. The finder switches are so arranged that the first finder is operated over a common start conductor to findthe first operated subscribers unit SU, and when it is found the start conductor is transferred to the second finder switch (not shown) so that the second finder will operate to find the second operated subscribers unit, and so on through the group. The trunk circuit TC is located at the operators position and is for the purpose of signalling the operator when the finder switch has been operated and has connected with a subscribers line. In this case the lamp L is lighted to signal the operator, who operates the key K to connect her headset across the line. The operation of the key K will extinguish the lamp and connect the operators telephone to the subscribers line. It should be noted, however, that the operators position need not be in the same exchange with the finder switchv FS and subsoribers units. The trunk conductors 73 and M may be the conductors of an inter-office or interexchange trunk. Relay 57 is acommon start relay and is maintained operated as long as one of the subscribers apparatus units is being used to extend a call to an operator. The relay 86 is a group busying relay and is operated only when all of the finder switches in the group are in use. It is arranged to render busy all the. subscribers lines actively associated with the secretarial equipment. The rectangle shown below the finder switch FS represents another similar finder. It should be noted that the start circuit reverts back to the first finder as soon as it is released;

The finder switch FSl andthe trunk circuit TCl, illustrated in Fig. 2 of the drawings, are modified forms of the finder switch FS and trunk circuit TC, respectively, Fig. 1. The finder FSl is similarto finder FS except that it has four wipers instead of three, the additional wiper being used as a control wiper to restore the wipers of the finder switch FSl to normal after each operation. The trunk circuit TCl is somewhat similar to trunk circuit TC shown in Fig. 1 except that it is provided with a rotary switch and associated lamp bank. This rotary switch is operated to advance its wipers in synchronism with the wipers of the rotary mechanism of the finder switch PS1 and is for the purpose of lighting lamps to give the operator visual indications of the subscriber unit (such as SU) that the finder switch PS1 has been rotated to. By referring to a card index, or a similar recording index, the operator is in a position to answer calls with the correct number of the called line or the subscribers name. This modification may be the preferred arrangement, particularly if this type of service is contracted for by professional men, for example, doctors, dentists, lawyers, etc-for the calling subscriber will be under the impression that the call is being answered by the wanted subscribers private secretary.

Detailed description The invention having been described in general, it will now be described in connection with a detailed description of operation. For this purpose it will be assumed that the subscriber at substation A has previously subscribed for secretary service. Therefore, his line has been connected at the distributing frame DF, by means of jumpers 34;,35, and 36, to the subscribers secretarial apparatus unit SU. It will also be assumed that the subscriber at substation A contemplates temporarily leaving the vicinity of his telephone and desires to have the secretarial operator in the exchange answer all his calls diu'ing his absence.

Conditioning the line of substation A for secretarial service The subscriber at substation A removes. his receiver and operates his calling device in accordance with a particular number, or digit combination, to control the switches in the exchange to establish a connection with the well-known ring-back switch, similar to the ring-back switch referred to in the above-mentioned Saunders patent. This connection is extended by way of the lineswitch LS and a selector, such as S, to a ring-back switch, such as PBS. After the subscriber has established the connection with the ring-back switch, the remaining ones of the dialled digits set the selected ring-back switch.

Having finished dialling, the subscriber hangs up his receiver. Since the operation of the exchange switches is well known, and the ring-back switch is described in detailv in the above-mentioned Saunders patent, it will suffice to say that the ring-back switch, depending upon the setting' imparted thereto, transmits ringing current of two frequencies, alternately, back over the calling subscribers line. It will be assumed that the two frequencies now selected are frequency 1 and frequency 2.

It may be pointed out that frequency 1 is the frequency for connecting the subscribers line for secretarial service, and frequency 2 is the frequency used for signalling regular individualline subscribers and for initiating the operation of the secretarial equipment to find the operated subscribers apparatus unit, while frequency 3 is the one used to revertthe line to regular use,

without secretarial service.

As above stated, the two ringing frequencies are alternately transmitted back to the subscribers line. Frequency relay 92, which is bridged across the subscribers line by way of conductors 60 and 61, is tuned to respondto frequency. 1. It responds to the ringing current of this particular frequency only, and at armature 37 and its working contact intermittently closes a circuit for the upper winding of relay 40. Relay 40 energizes over this circuit and locks itself up over the following circuit: ground, lower winding of relay 40, armature 45 and its front contact, winding of relay 41 and resistance 96 in multiple, and battery. Relay 41 does not energize over this circuit.

At armature 44 and its front contact, relay 40 bridges frequency relay 94 across the line conductors 60 and 61. Frequency relay 94 is tuned to respond to the same ringing frequency that operates. theringer at, substation A. Therefore,

gwhen frequency 2 is transmitted back over the calling line, the bell at substation A is rung and the frequency relay 94 responds. Responsive to the operation of frequency relay 94, an obvious circuit is, completed for energizing relay 43 over its upper winding. Relay 43 operates over this circuit and at its lightly adjusted armature and its front contact completes a locking circuit for itself over the lower winding. The locking circuit includes the normally closed contacts controlled by armature 52, armature 46 and its front contact, conductor 95, jumper 36 to the grounded release trunk conductor of the subscribers individual lineswitoh. At armature 54 and its front contact, relay 43 grounds conductor 62 by way of the upper winding of relay 42 and at armature 56 and its front contact it completes a circuit for the start relay 57. The shunt around theupper winding of relay 57, including armature 58, is for the purpose of making the relay slightly slow-to-operate and to permit the relay to release quickly when the circuit of the lower winding is open.

Operation of the finder FS Responsive to the operation of the start relay 57 a circuit is completed for the rotary magnet of the finder switch FS as follows: ground, armature 59 and its front contact, armature 6'? and its resting contact, winding of the rotary magnet 65, to battery. The rotary magnet 65 responds over this circuit and at its self-interrupting contact 97 completes a circuit for relay 63. Relay 63 operates and at armature 66 opens the initial energizing circuit for the rotary magnet 65. The rotary magnet restores, thereby advancing its Wipers YO-72 one step into engagement with the first set of bank contacts and at the same time it opens the energizing circuit for relay 63 at the self-interrupting contacts 97. Relay .63 falls back and at armature 66 again completes the energizing circuit for the rotary magnet 65.

Responsive to the inter-action of the rotary magnet and relay 63, the wipers -72 of the finder switch F3 are advanced step by step until the wiper 71 engages the bank contact grounded by way of the upper winding of relay 42 and conductor 62. When this occurs, a circuit is completed from ground, upper winding of relay 42, armature 54 and its front contact, conductor 62, wiper 71 of the finder switch FS, winding of relay 64, winding of relay 63, to battery. Relays 42 and 64 energize over this circuit, but relay 63 does not energize. Responsive to the energization of relay 64, the circuit for the rotary magnet 65 is opened at armature 67 and its resting contact and at the front contact of armature 67 the start circuit is extended to the next finder over conductor 91. therefore, the succeeding finder will be used the next time the start relay- 5'7 is energized. The circuit for the start relay 5'? is opened at armature 53 and its resting contact responsive to the energization of relay 42 in the above-traced circuit.

It should be noted, however, that if start relay 5'7 remains in its energized position due to the fact that a subscribers apparatus unit, such as SU, has been operated by another subscriber, the grounded start conductor 89 which is extended over conductor 96 to the next finder switch, due to the operation of relay 64, will cause the next finder switch to hunt for the conductor, similar to conductor 62, marked by the operation of the seized subscribers unit.

By .referrlng again to the operation of relay 42, it will be noted that it completes a locking circuit for its lower winding at armature 51 and its front contact, and the grounded conductor 95.

At armature 50 and at the normally closed contacts controlled by armature 52, relay 42 opens .the circuits for the upper and lower windings,

respectively, of relay 43 and at armature 52 and its front contact it extends locking ground potential to conductor 62, by way of resistance 98, and at armature 54 and its front contact it removes the ground by way of the upper winding of relay 42 from conductor 62. However, this conductor is now grounded by the circuit including resistance 98, as has been pointed out above. The high resistance 98 will prevent any other finder from stopping on this line but permits sufiicient current to flow to maintain the relay 64 in its energized condition.

Operation of trunk circuit TC By referring again to the operation of relay 64 it will be noted that at armatures 68 and69 and their respective front contacts it connects the line conductors 60 and 61 to the trunk line conductors 73 and '74. It will be observed that relay 75, in the trunk circuit TC, is bridged across the trunk conductors 73 and '74 and will respond to the ringing current that is intermittently transmitted over the subscribers line and conductors 60 and 61. At armature 78 and its front contact, relay completes a circuit forenergizing relay 7'7 as follows: from ground, armature 79 and its resting contact, armature '78 and its front contact, winding of relay '77, to battery. At armature 82 and its front contact, relay 7'7 completes a locking circuit for itself and it completes a circuit for lighting the lamp L at armature 81 and its front contact. The operator, upon noting the lighted condition of the lamp L, operates her answering key K, thereby bridging her telephone set across the line conductors '73 and 74. At contacts 85, of the key K, acircuit is completed for operating the slow-to-release relay 76. Relay 76 energizes and opens the locking circuit for relay 77 which accordingly falls back,

opening the circuit for lighting the lamp L. At

ring, the subscriber removes his receiver, thereby completing the talking connection between the subscriber at substation A and the operator in the central oflice. The subscriber at substation A gives the operator his name and telephone number and any other information the operator may need in order to intelligently answer incoming calls to the subscribers station during his absence. For example, the subscriber at substation A may instruct the operator to inform calling subscribers as to the time he expects to return, or the telephone number that the calling subscriber may call in order to get in touch with him; or he'may instruct the operator to get the name and telephone number of the calling subscriber so that he may call the party when he returns. The information the subscriber at substation A gives the operator, when he contemplates leaving the location of his telephone, de-

pends upon the business or profession that he is engaged in. 7

When the subscriber at substation A has given the secretarial operator the necessary information for answering incoming calls to his telephone, he will replace his receiver, thereby causing the release of the regular automatic switches (ring-back switch, selector, and the subscribers individual lineswitch) in the telephone exchange. Responsive to the release of the automatic switches in the exchange, ground is removed from conductor 95, thereby opening the locking circuit for relay 42, which accordingly falls back. In addition, the removal of ground from conductor 95 also causes the release of relay 64 in the finder switch FS. Upon falling back, relay 64 disconnects the start circuit which has been extended over conductor 91 to the next finder in the group and it connects the start circuit to the rotary magnet 65 of the finder switch FS, so that any subsequent calls will cause the finder switch F5 to be used. Relay 64 also opens the chain circuit extended to the next finder in the group over conductor 90 and disconnects the trunk circuit TC from the line conductors 60 and 61 at armatures 68 and 69 and their respective front contacts.

When the subscriber at substation A hangs up, the operator restores the answering key K to its normal position, thereby disconnecting the operators telephone circuit from the trunk conductors 73 and 74 and opening the circuit for the slow-to-release relay 76, which falls back. I

The finder switch FS and trunk circuit T0 are now available to connect up other subscribers for secretarial service and to connect up the secretarial operator so that she can answer incoming calls to subscribers connected up for secretarial service, as will be pointed out hereinafter.

It should be noted that after the subscriber at substation A replaces his receiver, relay 40 in the apparatus unit SU remains locked up over its lower winding in a circuit including the winding of relay 41 and resistance 96. Relays 41, 42, and 43 have all been restored to their normal deenergized positions. The purpose of maintaining relay 40 in its energized position is to maintain the frequency relay 94 bridged across the line conductors and 61 so that it can respond each time the bell at substation A is rung,

Incoming calls to conditioned line When a subscriber in the telephone exchange has dialled the proper digit to establish a connection with the subscriber at substation A, ringing current is transmitted for signalling the subscriber at substation A. In addition, the ringing current is also transmitted by way of jumpers 34 and 35 and conductors 6D and 61v to the frequency relays 92, 93, and 94. However, frequency relay 94 is the only one that is tuned to respond to the frequency of the ringing current that is being transmitted. Therefore, the ringer at substation A and the frequency relay 94 respond in synchronism to the ringing current transmitted over the line.

When the frequency relay 94 responds and closes armature 39 and its associated working contact, a circuit is completed for energizing relay 43 over its upper winding. Relay 43 energizes and locks itself by way of its lower winding over the previously traced circuit by way of conductor 95 which is now grounded by way of jumper 36 by the connector (not shown) used in establishing the connection. Relay 43 also connects the marking ground to the conductor 62, and completes a circuit for the slow-to-operate start relay 57 which accordingly energizes and places the start ground on conductor 89. I

Selecting the subscribers unit For the purposes of this description, it will be assumed that the finder switch FS has been operated to connect another subscriber, similar to the subscriber at substation A, with the secretarial operator in order to connect his line up for secretarial service. Therefore, the wipers --'72 of the finder switch FS will not be standing on the bank contacts to which the conductors 6062 are connected.

The grounding of the start conductor 89 causes the rotary magnet to operate and inter-act with relay 63 in the usual manner, thereby causing the wipers of the finder switch FS-to be rotated until the relay 54 is operated over a circuit including wiper 71 and the grounded conductor 62.

Relay 42 in the subscribers unit SU also responds and locks itself over its lower winding to the grounded conductor 95 and at the same time causes relay 43 to fall back, as has been described hereinbefore.

Signalling the secretarial operator The remaining operations take place in the usua1 manner, and it will suiiice to say that the trunk circuit TC is operated to signal the operator. The operator operates her answering key K to answer the call and to place the direct current bridge across the line in order to operate the ring-cut-oif relay in connector to disconnect the ringing current.

The operator finds out from the calling subscriber whom he is calling and ascertains from her card index or record what information she has been instructed to give a calling subscriber. In addition, the operator informs the calling subscriber that the wanted subscriber is not available at the present time. Depending on the circumstances, she will either inform the calling subscriber that she Will take the message or that she will notify the wanted subscriber of the call when he is available.

After the calling subscriber hangs up and the operator restores her answering key, the secretarial equipment restores to its normal position with the frequency relay 94 bridged across the line conductors 60 and 61 due to the fact that relay 40 is still maintained in its energized position over its lower winding.

It will thus be apparent that after the operator has answered a call intended for the subscriber at substation A, the equipment is in a position to respond to additional calls. Any subsequent calls for the subscriber at substation A will cause the ringer at his station to respond and, in addition, will cause the ringing relay 94 to respond in the manner described above to connect up the secretarial operator. Therefore, the operator is automatically connected up to answer all incoming calls to the subscriber at substation A, as long as the subscriber is connected up'for secretarial service.

Recalling the secretary from a conditioned line When the subscriber whose line is connected up for secretarial service desires to find out from the operator in the, exchange who has called him during his absence, he may do so in the following manner.

For the purpose of this description, it will be assumed that the subscriber has returned to the location of his telephoneand that he desires to find out from the secretarial operator who has called him during his absence. However, the subscriber does not desire to disconnect his line from secretarial service at the present time because he plans to leave the location of his telephone shortly. In order to establish connection with the secretarial operator, the subscriber sets up the connection over the regular exchange switches and the ring-back switch in the same manner as previously described. The ring-back switch. is set to transmit ringing current frequencies 1 and 2 in the manner described hereinbefore. i

The subscriber is accordingly connected to the secretarial operator and receives the desired information and then releases the connection. The operation of the secretarial equipment is exactly the same as has been described in connection with conditioning the subscribers line for secretary service, and it is not thought necessary to give the detailed operations of the apparatus again. When the subscriber hangs up and the secretarial operator disconnects, relay remains in its energized position as before.

When the subscriber is not in a position to make the call from his own station, he may go to any telephone station in the system and make ;a call to his own line-that is, he will dial his regular telephone number in the usual manner. The connection in this case is established in the same manner as has been previously described under the heading of Incoming calls to conditioned line. The subscriber receives the desired information and hangs up.

Removing the secretarial service condition from the line ofsubstation A device in the usual manner to establish a connection with the ring-back switch in the exchange. The subscriber then sets the ring-back switch in accordance with a particular code number'a'nd then hangsup his receiver. The proper ringing frequencies will be alternately transmitted back over his line to ring his bell in synchronism with the corresponding frequency relay 94 in the secretarial equipment and, in addition, will operate the frequency relay 93 so that the subscribers line will be disconnected from the scoretarial equipment after the subscriber and the operator have released their connection.

It will be assumed that the frequencies of the ringing current alternately transmitted back over thesubscribers line by the ring-back switch are frequencies 2 and 3.. When frequency 2 is transmitted, the bell at substation A and frequency relay 94 respond in the usual manner. As has beenpointed out hereinbefore, relay 43 responds. Responsive to the operation of relay 43, a circuit is completed for energizing start relay 5,7 to initiate the hunting movement .of the finder switch FS and a marking ground potential is applied to conductor 62.

When frequency 3 is transmitted, frequency relay 93, which is tuned to respond to this frequency, vibrates, thereby completing a circuit at armature 38 and its working contact for energizing relay 4.1 and at the same time placing a short circuit around the lower winding of relay 40, which, accordingly falls back. Upon energizing, relay 41 completes a locking circuit for itself by way of armature 48 and its front contact and the. grounded conductor 95, it maintains frequency relay 94 bridged across the line conductors and .61, and it prepares a locking circuit for relay &2 at armature i9 and its front contact.

The finder continues to rotate responsive to the above-mentioned operation of start relay57, until wiper "Z1 encounters the marked conductor 62. When thisoccurs, the connection is switched through to the trunk circuit TC and the operator is signalled, as has been described hereinbefore. The operator, upon noting thelightedcondition of the lamp L, operates her answering key K, thereby causing the operation of the ring-cut-oif relay in the ring-back switch. This operation disconnects the ringing currents from the calling subscribers line. When his bell stops ringing, the subscriber at substation A is accordingly informed that the operator has answered and he may remove his receiver to establish the talking connection. The subscriber asks the secretarial operator for the names and telephone numbers of subscribers that have called him during his absence and also for any other information the operator may have received. After the subscriber at substation A has received the information from the secretarial operator, he will hang up his receiver.

When the subscriber hangs up his receiver, all the operated switches used in establishing the connection release, and accordingly ground is removed from conductor 95. The removal of ground from conductor 95 opens the locking circuit for relays ll and 42, which accordingly fall back, thereby restoring the subscribers apparatus unit SU to its normal position.

It should be noted that when the subscriber operates the ring-back switch in order to disconnect his line from secretarial service, the frequencies ,of the ringing currents transmitted back over the subscribers line by the ring-backswitch are frequencies 2 and 3, and that after the connection between the operator and the subscriber is released, relay 40 is in its 'deenergized position. With relay 40 in its normal position, the frequency relay 94 is not bridged across the line. Therefore, frequency relay 94 cannot respond to the ringing current transmitted to ring the bell at substation A.

It will be understood that the subscriber at 135 substation A can again connect his line up for secretary service by dialling the particular series of digits to operate the ring-back switch to transmit the ringing frequencies 1 and 2 back over his line. This will cause the frequency relays 92 and 140 94 to respond in the manner pointed out hereinbefore and cause relay 4.0 to be locked up over its lower winding, thereby preparing a circuit for the frequency relay 9i so that it will respond each time thebell at subscribers station A is rung and 145 extend the call to the secretarial operator.

All secretarial trunks busy By referringtothe operation of relay 64, in the finder switch FS; it will be noted that at armature 99 and its front contact it connects ground potential to the conductor 90. Conductor 90 extends to a similar pair of contacts on a relay, similar to relay 64, in the next finder switch and so on through each finder in the group to the last finder switch FS. As each finder switch is operated to extend connections between a calling subscriber and the operator, a circuit is extended from each of the finders in turn, until the last one in the group is operated, and then to the busy relay 86. It is evident that when all the relays, similar to relay 64, have been operated in the manner pointed out above, that a circuit is completed from ground at the first finder switch FS, through the make contacts on the above-mentioned relays in the other finders, and then over conductor 88 and the busy relay 86 to battery. Relay 86 responds when this occurs and at the make contacts of all its armatures extends ground to the subscribers apparatus units, similar to apparatus unit SU, as will now be pointed out.

Let it be assumed that the subscriber at substation A has previously connected his line up for secretarial service in the manner previously described and that another subscriber in the exchange is attempting to call the subscriber at substation A. Since the subscriber at substation A is connected up for secretarial service, relay 40 is in its energized position, having been locked up over its lower winding in series with resistance 96 and the winding of relay 41 to battery. Therefore, when all the finder switches, similar to finder switch FS, are in use, relay 86 is energized as pointed out above. Ground is extended by way of armature 87 and its front contact, armature and its front contact, normally closed contacts controlled by armature 52, armature 46 and its front contact, to conductor 95. When the calling subscriber operates the connector to the line terminals to which the subscriber at substation A is connected, the test wiper of the connector will encounter ground by way of jumper 36 and conductor 95. When this occurs, the busy relay in the connector will operate and return busy tone to the calling subscriber. This will indicate to the calling subscriber that the wanted subscriber is busy; therefore, he will hang up his receiver and attempt to establish the connection some time later.

Operation of the modified apparatus A modification of the secretarial system shown in Fig. 1 will now be explained, attention being directed to the modified finder switchFSl and trunk circuit TCl illustrated in Fig. 2. In the modified secretarial system, the equipment comprising subscribers substation A, distributing frame DF, and subscribers apparatus unit SU shown to the left of the dotted line in Fig. 1 will be used, and the finder switch E81 and trunk circuit TCl, shown in Fig. 2, will be substituted for the equipment shown to the right of the dotted line in Fig. 1, it will be noted that the conductors .61, 62', 88, and 89' Will line up with conductors 60, 61, 62. 88, and 89 shown to the left of the dotted line in Fig. 1.

The modified circuits show a secretarial system in which the operator is informed, at the time a subscriber connects himself up for secretarial service, by means of an indicating lamp panel, of

the number of the trunk to which the subscriber connecting his line for secretary service is connected. With this arrangement the operator is always in a position to answer subsequent calls to the subscribers station, during the time the line is connected'up for secretarial service, either with the subscribers name or telephone number. The initial cost of installation of the modified improvement may be slightly higher than the system previously described. However, this arrangement, no doubt, is more efiicient for handling secretary service.

Conditioning line for secretarial service The operation of the subscribers apparatus unit SU to connect up the subscriber at substation A for secretarial service, to signal the operator when subsequent calls are'made to substation A, and to release the subscriber at substation A from secretarial service is the same as has been previously 90 described. Therefore, it will sufiice to say that responsive to the removal of the receiver by the subscriber at substation A and the subsequent transmission of the two different frequencies of ringing current by the ring-back switch, responsive to the dialling of the proper number, will cause the operation of frequency relays 92 and 92, the subsequent locking up of relay 40, the marking of conductor 62, and the operation of the start relay 57.

Responsive to the operation of the start relay 57, finder switch FSl is operated over the following circuit: ground, armature 59 and its front contact, conductor 89 of Fig. 1, conductor 89 of Fig. 2, armature 223 and its resting contact, armature 218 and its resting contact, armature 213 and its resting contact, winding of relay 202 to battery.

Operation of finder F81 and trunk circuitTC'I It might be well to point out at this time that if the finder switch FSl was in use and its wipers positioned to the contacts of a line being called or being connected up for secretarial service, re-' lays 205 and 206 would be in their operated positions. Therefore, the grounded start conductor 89' would now be extended over armature 223 and its front contact, armature 228 and its front contact, and conductor 91' to a finder switch similar to finder switch FSl which would accordingly advance its wipers to find the calling line.

Referring again to the operation of relay 202, it completes a circuit for rotary magnet 209, at armature 211 and its front contact, and it completes a circuit over the negative conductor 73' of the trunk line for relay 242, in the trunk circuit TCl, as follows: ground, armature 210 and its front contact, armature 214 and its resting contact, conductor 73' of the inter-connecting trunk line, armature 246 and its resting contact, winding of relay 242 to battery. Relay 242 operates over this circuit and at armature 255 and its front contact completes an energizing circuit for the rotary magnet 248 of the indicating switch. Responsive to the operation of rotary magnet 209 of the finder switch FSl a circuit is completed for relay 203 at the self-interrupting contacts 212 of the rotary magnet. Relay 203 responds over this circuit and at armature 213 and its resting contact "opens t e circuit for relay 202, whichaccordingly falls back. At armature 211 and its front contact, relay 202 opens the energizing circuit for rotary magnet 209 which accordingly falls back, thereby advancing the wipers 23423'7 of the finder switch PS1 into engagement with their associated first bank contacts.

Relay 202-also opensthe energizing circuit for relay 242, in the trunk circuit TCl, at armature 210 and itsfro'nt contact. Relay 242 falls back, thereby opening thecircuit of the rotary magnet 248 0-1" the indicating switch. Upon falling'back, 150

rotary magnet 248 advances its wipers 263265 into engagement with their associatedfirst bank contacts. a Responsive to the deenergization of the rotary magnet 209 the circuit for relay 203 is opened and therelay accordingly falls back and again completes a circuit for relay 202, which responds and causes the operation of the rotary magnet 209 at armature 211 and its front contact.

Therefore, every time relay 202 is energized it completes a circuit for rotary magnet 209 and relay 242, which operates rotary magnet 248. In addition, every time relay 202 falls back (responsive to the operation of relay 203) itv opens the energizing circuit for magnet 209 and relay 242. Magnet 209 advances its wipers one step and relay 242 opens the energizing circuit for magnet 248. Upon falling back, magnet 248 advances its wipers one step.

When the wipers of the finder switch FSl have been advancedstep by step until wiper 35 en-, counters the. grounded conductor 62 (grounded by way of conductor 62 and upper winding of relay 42 of the subscribers apparatus unit EU in Fig. 1)- a circuit is completed by way of grounded conductor 62, wiper 235 and its associated bank con--' tact, armature 215 and its resting contact, armature 227 and its resting contact, lower winding'of relay 205, to battery. Relay 205 responds and at armature 211 and its front contact completes a locking circuit for'its upper winding and at armature 223 and its resting contact it prepares the start circuit so that it can be transferred to the next finder in the group. Relay 205 also completes a circuit for relay 206, which accordingly energizes and transfers the start circuit over conductor 91', to the nextfinder of the group at armature 228 and its front contact. It should be remembered at this time that the relay 42 of the subscribers unit SU has been energized in series with relay 205 and that the start relay 57 is in its normal position. Therefore, the next time the start relay 57 is energized by a subscribers appa ratus unit, similar to subscribers apparatus unit 1 SU, the grounding of the start conductor 89 and 89 will not affect the finder FSl but will be extended over conductor 91 to the next finder switch in the group. The next finder switch in the group will hunt for theoperated subscribers unit in the same manner pointed out in connec tion with finder switch FSl. r a 7 Referring again to the initial energization'of relay 205, it will be noted that at armature 224 and its front contact it grounds conductor in the usual manner so that if all the finder switches of a group are in use the busy relay 86 is energized as has been hereinbefore described In addition, at armature 225 and its front contact (just prior to the operation of the slow-operatingv relay 206) conductor '74oi' the inter-connecting trunk line is momentarily grounded. This 'completes an energizing circuit for relay. 241 by way of armature 245 and its resting contact and the normally closed. contacts controlled by armature 251. Relay 41responds to this momentary application of ground and immediately locks itself up by way of armature 251 and its front contact and the grounded contacts associated with wiper 265 of the indicating switch. Relay 241 also opens a point in the circuit of the rotary magnet 248 of the indicating switchat armature 249 and its resting contact.

Operation of trunlccircuit TC I Since the relay 242 has been energizedtooper:

ate the rotary magnet 248 each time the relay 202 has been energized to operate rotary magnet 209, thewipers 263-26?) of the indicating switch have been advanced step by step and are now engaging the bank contacts corresponding to those engaged 'bythe wipers234-237 of the finder switch FSl. Therefore, responsive to the energization of relay 241 (which is energized when the calling line is found by the finder switch PS1) a circuit is completed by way of. ground at armature 250 and its front contact, armature 256 and its resting contact, armature 261 and its resting contact, lamp L1 to battery to signal the secretarial op erator. 1

7 Upon noting the lighted condition of the lamp L1, theoperator operates her'answering key K1, thereby completing the following circuit: ground, contacts 266 of the key Kharmature 247 and its front contact of operated relay 241, winding of relay 242 to battery. Relay 242 responds over this circuit, thereby opening the circuit to lamp L1 at armature 256 and its resting contact, com pleting the. energizing circuit for relay 243 at its front contact, and at armature 253 and its front contact completing the lighting circuit for the group lamp L3. The group lamp L3 is an indication to the secretarial operator of the particular group of trunks in which the calling line is located. Relay 243 respondsover the above-mentioned circuit and immediately locks itself in its energized position by way of the grounded bank contacts associated with the wipers 265 and armature 260 and its front contact. The initial energizing circuit for the relay is thereby opened at the normally closed contact controlled by armature 260. However, the ground connected to the contactassociated with wiper265 in addition to locking relay 243 in its energized position als completes a circuit for the lamp L3 and the par ticular tens and units lamps connected to the bank contacts engaged by wipers 263 and 264.

Since the wipers 263 and 264 have advanced in synchronism with the'wipers of the finder switch F81, these wipers are now positioned to correspending contacts. The operator, noting the numbers of the lamps that are lighted, is thereby informed of the number of the trunk that the finder switch FSl is associated with. At contacts 267 and 268 of the key K1, the operators telephone set is bridged across the trunk conductors 73' and 74.

Responsive to bridging of the operators telephone set across the trunk conductors, relay 208 in'the finder switch PS1 operates over the following circuit: ground, lower winding of relay 208, armature 229 and its front contact, lower line trunk conductor 74, contacts 268 of the key K1, operators telephone loop, contacts 267 of the key K1, armature 246 and its front contact, upper trunk conductor 73', armature 226 and its front contact, upper winding of relay 208 to battery. Relay 208 responds and completes an obvious energizingcircuit for relay 207 which also responds.

. At armature231 and its front contact, relay 207 connects the impedance 201 across the line conductors of the trunk, thereby causing the ring-cut-oif relay in the ring-back switch to function and disconnect the ringing currents from the calling subscribers line. In addition, relay 207 completes an energizing circuit for relay 204 at armature 232 and its front contact, at armature 230 and its front contact it extends the upper 'line'conductor 60' through to the upper trunk conductor 73', thereby completing the con-' nection between the calling subscriber and the operator, and atarmature238 andits front contact it closes anotherpoint in the circuit of relay 208.

Responsive to the energization of relay 204, a locking circuit is completed for itself by way of armature 217 and the grounded bank contacts associated with wiper 236; the locking circuit for relay 205 is openedat armature 216 and its resting contact; a circuit is prepared at armature 219 and its front contact for maintaining the start circuit for the next finder closed after relay 205 lalls back; and another point is closed in the busying circuit over conductor 90' at armature 220 and its front contact. Responsive to the opening of the locking circuit for the upper winding of relay 205, it falls back, thereby opening the circuit forrelay 206, which also restores. In addition, relay 205 completes a new circuit for extending the start conductor .89 to the next finder over conductor 91 at armature 223 and its'resting'contact.

When the bell'of the calling subscriber ceases to ring, the subscriber removes his receiver and is thereby connected through to the secretarial operator. Since the operator is informed,'byreferring to her card index, of the name and telephone number of the subscriber connected to the trunk indicated by the lighted lamp, the-subscriber can either hang up without talking to the operator or he can talk to the operator to give her any information that may be necessary to answer the subscribers incoming calls intelligently.

When this information has been given to the operator, the calling subscriber hangs up his receiver, thereby causing the release of the subscribers apparatus unit SU in the manner previously described. However, relay 40 remains locked up in a circuit including its lower winding, armature 45 and its front contact, winding of relay 41 and resistance 96 in multiple, and battery. This maintains the frequency relay 94 bridged across the subscribers line so that it can respond each time the subscribers belllis rung.

After the subscriber hangs up his receiver, the operator may release the connection in the following manner:

. Restoration of the finder F81 and the "trunk circuz't TC1 In order torelease the connection, the operator restores her key K1 to its normal position. Responsive to the removal of ground at contacts 266 of the key Kl, relay 242 restores to normal. Responsive to the deenergization of relay 242, a circuit is completed at armature 252 and its resting contact to prevent the relays and wipers of the finder switch FSl from returning 1 to normal by bridging the trunk conductors 73' and 74' by way of the resistance 244. This circuit maintains relay 208 in its energized position. This is for the purpose of preventing the finder switch PS1 from starting its release movement until the equipment in the trunk circuit 'ICl has been restored'to normal.

At armature 255 and its resting contact, relay 242, upon deenergizing, completes the self-interrupting circuit for rotary magnet 248 of the indicating switch as follows: ground, contactsassociated with the wiper265, wiper 265, armature 260 and its front contact, self-interrupting contact 254 of the rotary magnet 248, armature 2'55 and its resting contact, winding of rotary magnet 248, to battery. Magnet 2'48-res'ponds over this circuit and interrupts its energizing circuit at its self-:interrupting contact 254, thereby opening its circuit and advancing the wipers one step. When the-magnet deenergizes, the circuit is again completed at the self-interrupting contact 254 and the action is again repeated. The wipers 263, 264, and 265 are accordingly advanced step by step until the wiper 265 encounters the ungrounded bank contact of the home position. When this occurs the circuit for operating the rotary magnet248 is opened due to the fact that the wiper 265 no longer encounters the ground potential. In addition, the energizing circuits for relays 243 and 241 are opened and the relays accordingly release. At armature 262 and its front contact, relay 243 also opens the circuit for the slow-to-release relay 240 which subsequently falls back, thereby bringing the equipment in the trunk circuit TCl to its original starting position.

At armature 257 and its front contact, relay 243 opens the loop circuit for relay 208, of the finder switch FSl, which accordingly falls back and opens the circuit for the slow-to-release relay 207 at armature 233 and its front contact. Relay 207 subsequently falls back and disconnects the relay 208 from the trunk line conductors 73 and 74'.

Since the equipment in the trunk circuit TCl has now been restored to'normal and has caused the release of relays 207 and 208 in the finderv switch FSl, the restoration of the finder'switch F51 will now be explained. Responsive to the release of relay 207, the stepping relay 202 is energized over the following circuit: ground, contacts associated with the wiper 236, wiper 236, armature 232 and its resting contact, armature 218 and its front contact (relay 204 being locked up to the grounded wiper 236) armature 213 and its resting'contact, winding of relay 202 to battery. Responsive to the energization of relay 202, an energizing circuit is completed for the rotary magnet 209, which responds and completes the circuitfor relay 203 at its self-interrupting contact 212. Relay 203 energizes and at armature 2-13 and its resting contact opens the initial energizing circuit for relay 202, which accordingly falls back and opens the energizing circuit for the rotary magnet 209 which also falls back, advancing the wipers one step. Responsive to the deener'gization of the rotary magnet 209, the circuit for relay 203 is opened. Relay 203 falls back and again completes the circuit for relay 202. This inter-action of the relays and the rotary magnet continues until the wipers are returned to their normal home position.

Although the operationof relay 202 causes armature 210 and its front contact to close each time it is energized, this operation'has no effect at this time due to the fact that relay 204 remains locked up by way of the grounded wiper 236. However, when the wipers are returned to their normal position, wiper 236 no longer encounters ground, thereby causing relay 204 to restore, "and, in addition, removes the operating ground for relay 202. The relays and wipers of 140 the finder switch FSl are now restored to their normal starting position and maybe again operated to connect up a calling line for secretarial service or to find a line on secretarial service that is being called.

Incoming calls to conditioned line When a-subscriber desiring to establish a connection with the subscriber at substation A has manipulated his-calling device and has finally set his connector to the called line and the connector transmits the ringing current for signalling the subscriber at substation A, the frequency relay 94, which is now bridged across the line by way of contacts 44 of the energized relay 40, responds and causes the operation of the start relay 5'7 and the marking of conductor 62 in the same manner described hereinbefore. The finder PS1 will automatically rotate to find the 'called line and at the same time causes the indicating switch in the trunk circuit TCl to operate in synchronism. When the markedline is reached by the finder F51 and the indicating switch in the trunk circuit TCl is brought to rest, the operator is signalled. The operator receives the calling signal and in addition ascertains from her indicating lamp bank the number of the trunk seized. By referring to her card index, she will be informed that the trunk seized is the one to which the subscriber at substation A is connected up for secretarial service. Since the operator has been previously informed of the subscribers name and telephone number, she may answer the call accordingly.

The operation of the equipment when the operator answers a call for a subscriber that is connected up for secretarial service is exactly the same as has been described in connection with answering a call to a subscriber connecting his line up forsecretarial service. Therefore, it will suffice to say that the operator answers the call by giving the name or the telephone number of the Wanted subscriber and receives any information the calling subscriber desires to have forwarded to the subscriber at substation A or gives the calling subscriber any information that the subscriber at substation A has informed the operator to forward to any calling subscribers.

After the calling subscriber hangs up, the operator restores her key K1 in the usual manner, thereby causing the indicating switch in the trunk circuit T01 and the finder switch FSl to restore to normal, in the same manner described hereinbefore.

All subsequent calls to the subscriber at substation A are answered by the operator at the telephone exchange in the same manner. Attention is called to the fact that relay 40 of the subscribers apparatus unit SU remains locked up during the entire period that the subscriber at substation A is connected up for secretarial service and is released only when he desires to have his line disconnected from secretarial service.

Removing the secretarial service condition from the line of substation A When the subscriber at substation A returns or is in a position to answer all his telephone calls, he will set up a connection to the main exchange switches to cause the ring-back switch to transmit the ringing frequencies for disconnecting his line from secretarial service in the manner described hereinbefore. The finder switch PS1 is operated in the usual manner to find the marked lineand, in addition, transmits impulses over the upper line conductor '73 to operate the indicating switch in the trunk circuit T01. switch in the trunk circuit TCl operate in synchronism in the usual manner, the former to find the marked line and the latter to light the lamps to indicate to the operator the number of .the trunk selected by the finder FSl. The operator is signalled in the usual manner and operates her key Kl, thereby completing the talking ;to the operator. nect his line from secretary service, he will oper- The finder switch PSI and the indicating connection between the subscriber at substation Aand the operator. After the subscriber at substation A has been informed of the names and possibly telephone numbers of the subscribers that have called him during his absence or during the, period he has been connected up for secretarial service, he hangs up his receiver. The operator restores her key K1 and causes the indicating switch in the trunk circuit TCl and the finder PS1 to restore to normal.

After the connection is released, relay 40 is no longer operated and the frequency relay 94, which is tuned to the same frequency as the bell at substation A, is no longer bridged across the line conductors 60 and 61; Since the frequency relay 94 no longer is bridged across the line conductors 60 and 61, the subscriber at substation it will have to answer all subsequent calls to his me. a l It should be noted that when the secretarial equipment of this invention is connected up to give secretarial service to a subscribers line the subscriber is always informed of calls to his line due to the fact that his bell responds to the ringing current transmitted by a calling subscriber. In addition, the secretarial equipment is started in the usual manner and finally completes the connection to the operator; However, should the subscriber desire to answer his own call, he may do so merely, by removing his receiver. The operator upon answering the call will 'find that the subscriber has already answered and disconnects her telephone set from the connection merely by restoring her answering key to its normal position.

One case in which this invention may find considerable application is that of a subscriber who may, for example, be a doctor. The doctor will receive his own messages while he is at his office, but he may desire the service of the telephone operator to receive any messages intended for him during his absence. Thus, by setting up the automatic switches so that the ring-back switch will transmit the proper ringing frequencies, the telephone operator will be in a position to receive all calls intended for him. If the doctor should desire to know at any time who has called him, he may step to any telephone in the system and call his own number and will be automatically connected up to the operator in the same manner that subscribers attempting to establish a connection with his line are connected. The doctor informs the operator that he desiresto know who has called him, and receives the information, When the doctor returns to his ofiice, he may call the operator by setting-up the automatic switches to transmit the proper ringing frequencies to connect him If he does not desire to disconate the switches so that the ring-back switch will transmit the proper ringing frequencies, while on the other hand if he desires to have his line disconnected he will-cause the ring-back switch to transmit different ringing frequencies.

Secretarial service for a party-line subscriber Secretarialservice can be given to a subscriber on a partyline if it is necessary to do so. The ring-back switches are generally equipped to transmit five different frequencies of ringing current.. Since two frequencies-(frequencies 1 and 3) are required for connecting and disconnecting the secretarial equipment and another frequency (frequency 2) is used for signalling a subscriber connected up forisecretarial service and to control the secretarial equipment to find the line whenanincoming call is received, two frequencies (frequencies 4 and 5) are not in use. Therefore, two more subscribers can be connected to the same line, making atotal of three parties on the same line. It is evident from the foregoing that the secretarial equipment can be controlled to intercept incoming calls for the subscriber on the party line whose ringing frequency is frequency 2, but will not respond when the other two parties on the line, whose ringing frequencies are frequencies 4 and 5, are called.

It should be noted that frequency relay 94 respends only to the same frequency of ringing current that the ringer at the substation connected up for secretarial service responds to. In the present embodiment, frequency 2 has been used throughout for signalling the contracting subscriber. If :the contracting subscribers ringer responds to frequency 4, then the frequency relay 94 in the secretarial equipment must be tuned to respond to frequency 4.

While the invention has been described in two particular embodiments merely for the purpose of illustration, it will be apparent that the general principles'of this invention may be applied to other and widely varied circuit organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. In a telephone system, secretarial equipment in the exchange, a line, a subscribers station connected to said line, means controlled from said station for connecting said equipment to said line, an operators position, means responsive to a call from said subscribers station for control; ling said equipment to extend said call to said position, and means controlled by the frequency of the ringing current used when said call is extended for either maintaining said equipment connected to said line or for disconnecting the same when the call from said subscribers station is released.

2. In a telephone system arranged for secretarial service, an operators position, a subscribers station, means under the control of said subscribers station for extending a connection from said station to said operators position, and means responsive thereto and effective after the said connection has been released for extending subsequent calls incoming to said station to said operators position.

3. In a telephone system arranged for secretarial service, an operators position, a subscribers station, means under the control of said subscribers station for extending a connection from said station to said operators position, means responsive thereto and effective after the said connection has been released for extending subsequent calls incoming to said station to said operators position, and means under the control of said station, operable at the will of the subscriber thereat, for nullifying the said effect of the first-named connection.

4; In a telephone system, a subscribers station, secretarial equipment in the central oflice, means controlled by the subscriber at said station for connecting his line with said equipment to establish a talking connection with the secretarial operator, means for maintaining said line connected to said equipment after said connection is released, means responsive thereafter each time an incoming call for said station is received for signalling said operator, and means responsive when station hangs up, and means responsive to said 1 rin ing currents for signalling the subscriber at said station and for signalling the operator at said position. 1

6. In a telephone system, a subscribers station connected to a line, central orifice switches," an operators position, means at said station for -con-' trolling the central office switches to alternately transmit ringing currents of two diiferent frequencies over said line after the subscriber; at

said station hangs up, means responsive to said ringing currents for signalling the subscriber at said station and for signalling the operator at said position, and means responsive when said-operator answers for disconnecting said ringing currents.

7. In a telephone system, a subscribers'station connected to a line, central office switches, an operators position, means at said station for controlling the central oflice switches to alternately transmit ringing currents of two different frequencies over said line after the subscriber at said station hangs up, means responsive to said ringing currents for signalling the subscriber at said station and for signalling the operator at said position, means responsive when said operator answers for disconnecting said ringing currents, and means responsive when the subscriber at said station answers for establishing a talking connection with said operator.

8. In a telephone system, a subscribers station connected to a line, central oiiice switches, an operators position, means at said station for controlling the central oifice switches to alternately transmit ringing currents of 'two different frequencies over said line after the subscriber at said station hangs up, means responsiveto said ringing currents for signalling the subscriber at said station and for signalling the operator at said position, means responsive when said operator answers for disconnecting i said ringing currents, means responsive when the subscriber at said station answers for establishing a talking connection with said operator, and means responsive when said subscriber hangs up for releasing said central office switches.

9. In a telephone system, secretarial equipment comprising a plurality of subscribers apparatus units each of which is associated with a different subscribers line, means controlled from each of said subscribers stations for connecting his associated unit to his line, a; finder switch, an operators'position having a rotary switch thereat, means responsive to the operation of one of said units for operating said finder and said rotary switch in synchronism, means including the finder for selecting the operated unit andfor extending the associated'subscribers line to said position, and means including said rotary switch for lighting certain lamps to indicate to the operator the number of the line selected by said finder.

10. In a telephone system, secretarial equipment comprising a plurality of subscribers apparatus units each of which is associated with a different subscribers line, means controlled from each of said subscribers stations for connecting his associated unit to his line, a finder switch, an operators position having a rotary switch thereat, means responsive to the operation of one of said units for operating said finder and said rotary switch in synchronism, means including the finder for selecting the operated unit and for extending the associated subscribers line to said position, means including said rotary switch for lighting certain lamps to indicate to the operator the number of the line selected by said finder, and means at said operators position for establishing a talking connection with the subscriber on said line.

11. In a telephone system, secretarial equipment comprising a plurality of subscribers apparatus units each of which is associated with a difierent subscribers line, means controlled from each of said subscribers stations for connecting his associated unit to his line, a finder switch, an operators position having a rotary switch thereat, means responsive to the operation of one of said units for operating said finder and said rotary switch in synchronism, means including the finder for selecting the operated unit and for extending the associated subscribers line to said position, means including said rotary switch for lighting certain lamps to indicate to the operator the number of the line selected by said finder, means at said operators position for establishing a talking connection with the subscriber on said line, means responsive when said connection is released for automatically advancing the wipers of said rotary switch to restore the same to the original starting position, and means responsive to the restoration of the wipers of said rotary switch for automatically advancing the wipers of said finder switch to restore the same to the original starting position.

12. In a telephone system arranged for secretarial service, a party line, a subscribers station on said line connected up for secretarial service, a finder switch, an operators position having an associated rotary switch, means responsive to the ringing current transmitted on an incoming call to said station for operating said finder switch to find said line, and means for operating said rotary switch in synchronism with said finder to give the operator at said position visual indications of the number of the line selected by said finder.

13. In a telephone system arranged for scoretarial service, a party line, a subscribers station on said line connected up for secretarial service, a finder switch, an operators position having an associated rotary switch, means responsive to the ringing current transmitted on an incoming call to said station for operating said finder switch to find said line, means for operating said rotary switch in synchronism with said finder to give the operator at said position visual indications of the number of the line selected by said finder, and means at said position for answering the incoming call for the subscriber on said line.

14. In a telephone system, a line, a plurality of subscribers stations on said line, means for selectively signalling the subscribers on said line, a device, an operators position, means controlled from one of the stations on said line for connecting said device to said line, means responsive to the particular ringing current transmitted by a calling subscriber to signal the subscriber at said station for operating said device, and means responsive to the operation of said device for extending said call to said operators position.

15. In a telephone system, a line, a plurality oi. subscribers stations on said line, a device for extending calls to an operators position, means controlled by a particular station on said line for connecting said device to said line, and means responsive to an incoming call to said particular station for operating said device.

16. In an automatic telephone system which includes party lines and ring back apparatus for handling revertive calls, a plurality of lines equipped for secretary service, a secretarys position, and means whereby a subscriber on one of said plurality of lines can pre-set the secretary service equipment of his line by means of said ring back apparatus so that incoming calls to his line are transferred to said secretarys position.

17. In an automatic telephone system, a subscribers line, a second line, means for automatically extending a call incoming to said subscribers line to said second line, said means being normally non-responsive to such incoming call, a ring back switch accessible to said subscribers line, and means controlled by ringing current received back from said switch when the same is connected with for rendering said means responsive.

18. In an automatic telephone system, a subscribers line, a second line, means for automatically extending a call incoming to said subscribers line to said second line, said means being normally non-responsive to such incoming call, a ring back switch accessible to said subscribers line, means controlled by ringing current received back from said switch when the same is connected with for rendering said means responsive, and means controlled by ringing current of a different frequency received from said switch on a later connection thereto for restoring said means to its normal non-responsive condition.

19. In a telephone system, a subscribers line, two ringing current responsive relays bridged across said line, said relays being tuned to different frequencies, means including ring back apparatus controlled over said line to transmit back to the line the proper ringing current to operate either of said relays as desired, and a third relay which is connected to said line responsive to the operation of one of said tuned relays and which is disconnected therefrom responsive to the opera- 1 tion of the other tuned relay.

FREDERICK L. KAHN. 

